Carnuntum (Καρνους, Carnous in Ancient Greek according to Ptolemy) was a Roman Legionary Fortress or castrum legionarium and also headquarters of the Pannonian fleet from 50 AD. After the 1st century it was capital of the Pannonia Superior province. It also became a large city of 50,000 inhabitants.[1][2]

Significant Romanisation occurred when the town was selected as the garrison of the Legio XV Apollinaris before 14 AD.[3] A few years later, it became the centre of the Roman fortifications along the Danube from Vindobona (now Vienna) to Brigetio (Ó-Szőny). According to Tacitus,[4] the emperor Claudius ordered the governor of Pannonia "to have a legion with an auxiliary on the bank of the Danube" to protect the losers of a dispute between Germanic tribes (the Quadi and Marcomanni) and deter the victors from the temptation to invade Pannonia. To this period (about 50 AD) belongs the auxiliary castrum of a cavalry ala 1.5 km south-west of the legionary fortress.[5]

In 71 AD, after several campaigns, the Legio XV Apollinaris returned to Carnuntum and rebuilt its fortress. While some of the legion fought in Trajan's Dacian Wars, the main body of the legion remained in Pannonia.

In the Severan dynasty (193-235) Carnuntum experienced an economic boom, the canabae reaching its maximum size. Caracalla elevated it to colony status as Septimia Colonia Aurelia Antoniana.[9] During the reign of Gallienus, the Pannonians rebelled by electing the usurper Regalianus who established a mint whose coins depicted him and his wife Sulpicia Dryantilla. He was killed shortly afterwards by his own soldiers probably at Carnuntum.[10][11]

In 374 it was destroyed by Germanic invaders, the Quadi and Iazyges. Although partly restored by Valentinian I,[14] it never regained its former importance, and Vindobona became the chief military centre. During the Barbarian Invasions, Carnuntum was eventually abandoned and used as a cemetery and source of building material for building projects elsewhere.

The remains of the civilian city extend around the village Petronell-Carnuntum. There are several places to see in the city: Roman city quarter in the open-air museum, palace ruins, amphitheatre, and "Heidentor".

The Roman city ruins are exposed in the open-air museum directly in the present village. One of the ancient houses, called the House of Lucius, has been rebuilt using traditional techniques. It was opened to the public on 1 June 2006.

The (forum) was next to the palace ruins, also referred to as the large public baths.

Some way outside the city was a large amphitheatre, which had room for about 15,000 spectators.
A plate with an inscription found at the site claims that this building was the 4th largest amphitheatre in the whole Roman Empire.

Between 354 AD and 361 AD a huge triumphal monument was erected next to the camp and city. Contemporary reports suggest that Emperor Constantius II had it built to commemorate his victories. When the remains of Carnuntum disappeared after the Migration Period the monument remained as an isolated building in a natural landscape and led Medieval people to believe it was the tomb of a pagan giant. Hence, they called it "Heidentor" (pagan gate).

In September 2011 aerial photographs and ground-penetrating radar led to the discovery of the typical contours of an ancient Roman gladiator school to the south of the Roman settlement, a ludus rivaling the Ludus Magnus school and covering an area of some 3,350 square yards (0.280 ha).[15] This approach of aerial photography and modern remote sensing has allowed for a detailed virtual recreation of the gladiator school.[16] The aerial photographs used in the recreation were acquired with a radio-controlled Microdrone md4-1000 quadrocopter, which captured a sufficient amount of photographs to create an overlap among them. Then, using a technique called Structure from Motion (SfM), a 3D model of the school was calculated using the sharpest images.[17]
The school, along with the amphitheater, was located outside of the town's walls. The school had training grounds, bathing facilities, an assembly hall and dormitories for the gladiators. The school also had a courtyard which housed a training area for gladiators. The school was attached to an open campus which was most likely used for chariot races.[18]